Along with the increase of the size of the thin film transistor liquid crystal display (TFT-LCD), uneven display will occur due to an IR-drop in the case that an electrode and a signal transmission line of the display each have a relatively large resistance. Hence, the signal transmission line and the electrode need to be made of a material having low resistivity, and usually a wire for the display is made of Cu.
In the case that the signal transmission line and the electrode are made of Cu, Cu atoms therein may easily be diffused into an insulation layer, thereby an insulation characteristic of the insulation layer may be adversely affected. At this time, usually a metal barrier layer needs to be provided, so as to prevent the diffusion of Cu. However, during the manufacture of an array substrate, an etchant for etching the metal barrier layer may destroy a semiconductor layer of the TFT, and as a result, the image quality of the display will be adversely affected.